Vaccines and autism

In the 1990s some concerns arose about the safety of the MMR vaccine and a possible link with autism. Autism is one of a range of neurodevelopmental disorders, called autism spectrum disorder (ASD); those affected with ASD can show differences in how they learn, behave and communicate with others. Since then there have been hundreds of studies that have proven that there is no evidence that the MMR vaccine causes ASD.

The World Health Organisation commissioned a review of studies that had looked at a possible link between ASD and the MMR vaccine; they concluded that there is no evidence that the MMR vaccine causes ASD. Some examples of these studies include a study of all children born in Denmark between 1991 and 1998 (over 537,000 children) who either received the MMR vaccine or were not vaccinated with it. The authors (Madsen et al. 2002) found no increase in ASD in the children vaccinated with MMR over those who were unvaccinated.

Another example is a study by DeStefano et al. who compared the number of vaccines received by two groups of children, those with ASD and those without ASD, because of some concerns that children’s systems are ‘overloaded’ with the number of vaccines received in childhood. The authors found no link between the development of ASD and the number of vaccines received during the first 2 years of life, and no link between ASD and the number of vaccines received on any one day.

Some parents were also concerned that a vaccine ingredient, thimoserol (a preservative), could cause autism. However, meta-analyses and a number of other large studies including those by the Centres for Disease Control (CDC) in the USA have found no link between thimoserol and autism or any other neurodevelopmental disorders. Because of the initial worries, as a precaution thimoserol was removed from most vaccines while safety studies were carried out. It is now used in very few vaccines even though it was found to be completely safe.

A huge meta-analysis was conducted on over 1,000 independent studies into the link between childhood vaccination and ASD. A meta-analysis is a statistical analysis of a large number of scientific studies. There were more than 1.2 million children included in this meta-analysis which concluded that there was no evidence of a link between ASD and childhood vaccinations, the MMR vaccine, thimoserol or mercury.

Unfortunately, due to the misinformation that is still circulating some parents do not vaccinate their children and we are starting to see the resurgence of diseases that had been under control. In early 2015 there were over one hundred cases of measles in the USA that were linked to one unvaccinated child with the measles who attended a theme park in California. Several of those who contracted measles in this outbreak (either from attendance at the theme park on that day or by close contact with infected family members) were babies too young to have received the MMR vaccine.

It is essential that all healthy members of society are vaccinated in order to protect the vulnerable members such as young babies and those with compromised immune systems.